In fabricating typical microelectronic devices, certain objects are often transferred between various locations within a work environment by robotic handling systems. These objects frequently include substrates or wafers for forming microelectronic devices. They may be substrates including partially or fully completed microelectronic devices, cassettes or other carriers, or other objects needed to be moved between different locations. The robots used must be able to pick up objects from a particular location such as a cassette or other carrier, processing station, another robot, or an entry/exit station, and then transfer them to a desired location. Usually, these robots include an end effector mounted to an end of a robot arm to facilitate transfer of such objects. These transfers desirably take place without crashing the robot or damaging the objects and are desired to occur quickly so as to maximize production throughput. In other words, rapid and accurate robot movements are desired. In order to perform these transfers, the robot generally needs to accurately know the spatial coordinates of at least some portion of an end effector and/or other components with respect to the spatial coordinates of the pickup and destination positions.
Generally, a robot body is fixed to a base support and an articulated robot arm is cantilevered from the robot body. The robot arm includes a first arm section pivotably attached to a second arm section. A wand or end-effector, whose outer end is generally y-shaped with spaced apart fingers, is pivotably attached to the second arm section. Vacuum ports (not shown), or edge gripping mechanisms, are usually provided on the end effector, which enable it to retain a wafer in order to pick up and transport the wafer from a cassette to a process station and vice-versa. In other instances, the robot base is not fixed but rather is moveable along track(s) or the like.
Robot mechanisms can have one or multiple degrees of freedom. The number of degrees of freedom of a robot corresponds with the number of independent position variables that must be specified to locate all parts of the mechanism. For example, robotic systems having three degrees of freedom have been used because of their relative simplicity. One such three-axis robot is described in U.S. Pat. No. 6,242,879 to Sagues et al. The Sagues et al. robot has three axes of movement, which allow the robot to move in the radial (R), angular or theta (Θ), and vertical (Z) directions.
More complex robotic systems having six or more degrees of freedom are utilized as well. In most robots, the links of the robot form an open kinematic chain, and because each joint position is usually defined with a single variable, the number of joints corresponds with the number of degrees of freedom. As such, robots with 6 or more degrees of freedom can move in x, y, z, yaw, pitch, and roll.
In typical systems, the general geometry of the robot and the various process stations is known. That is, the approximate dimensional relationships between the robot and each location of interest are known, within nominal tolerances, from design specification or physical measurements. Generally, however, such information may not be accurate enough to assure that the robot can operate properly without damaging any systems component or the objects being handled. In order to assure the close tolerances required for the necessary precision during object transfer, a robot positioned within a working environment is usually taught where certain locations of the environment are. This teaching can be manual, semi-automated, or fully automated. Robot teaching or robot calibration, if automated, is referred to as autoteaching or autocalibration. Additionally, whenever the system is serviced or a machine component wears, settles, or malfunctions and requires replacement, upgrade, or service, the robot must be re-taught positions relative to the modified component(s) because the robot cannot automatically adapt to such variations. If the robot is not re-taught properly within close tolerances, serious damage to the robot or loss of expensive objects such as wafers or objects can result.
Manual teaching typically occurs without the help of sensors on the robot and/or sensors distributed around the environment of the robot. Besides consuming many hours, manual teaching procedures can introduce subjectivity, and thus a significant possibility for errors. This creates a problem of reproducibility.
Thus, automated procedures would be more desirable in many applications. One example of an automated approach for teaching a wafer transfer robot can be found in U.S. Pat. No. 6,075,334 to Sagues et al. This patent purportedly describes a system for automatically calibrating a wafer handling robot so that the robot can move wafers among precise locations within the range of motion of the robot. The system includes a controller having memory and logic sections connected to a robot having an articulated arm that is movable in three degrees of movement. Dimensional characteristics of the robot wand and the enclosures are stored in the controller memory.
The robot of U.S. Pat. No. 6,075,334 uses a thin beam laser sensor, a continuous beam sensor, and a reflective LED sensor. These sensors are provided at each enclosure and/or the robot wand, which are activated and then provide signals to the controller that are relative to the wand position. The robot is programmed to execute a series of progressive movements at each enclosure location, which are controlled by a combination of sensor response signals and the appropriate dimensional characteristics. At the end of the programmed movements, the robot wand is positioned within a process station or cassette so that it can engage for removal or release an object therein at a precise predetermined location.
Another automated approach for teaching a wafer transfer robot can be found in U.S. Pat. No. 6,242,879 to Sagues et al. In this patent a method and apparatus for automatically calibrating the precise positioning of a wafer handling robot relative to a target structure is described. The apparatus includes a machine controller connected to a robot having an end-effector with three degrees of movement. The controller has a memory with stored approximate distance and geometrical data defining the general location of structural features of the target structure. The robot is programmed to move toward the target structure in a series of sequential movements, each movement culminating with the robot end-effector touching a preselected exterior feature of the target structure. Each touching of the end-effector is sensed by utilizing motor torque variations. This provides data for the controller, which then calculates the precise location of the target structure. The data accumulated during a series of touching steps by the robot end-effector is utilized by the controller to provide a precise calibrated control program for future operation of the robot.
The light beam sensor approach and the torque sensing approach described in U.S. Pat. No. 6,075,334 to Sagues et al. and U.S. Pat. No. 6,242,879 to Sagues et al. suffer from several limitations. In particular, both approaches can be difficult to utilize with robots having more than three degrees of movement as more degrees of motion generally require more numerous and complex sensing movements. Increased complexity of the sensing approach can be expensive and can introduce difficulties in calibration and teaching especially where precise sensing is not possible. Moreover, motor torque sensing is generally limited to single axis motion such as planar motion for teaching of slots of a cassette. Thus, this type of sensing cannot handle non-planar motion such as is required for accommodating multiple entry angles for certain cassettes or the like.
Touch sensitive devices, also referred to as “tactile sensor devices,” “touch screens,” “touch pads,” or “touch panels” are widely used in many applications, including computer interfaces, personal data assistants, cellular telephones, and the like. Touch sensitive devices allow a user to interface with a machine by touching a surface of the device. These devices use several technologies to determine the position of a touch on the surface. Advantageously, these devices not only detect the occurrence of a touch, but the location of the touch as well. Common technologies used include electrodes, resistive networks, surface acoustic waves, and other types of technology. The tactile sensing or touch-sensitive device translates the touch location to input signals for processing by a computer or other device. For example, certain touch sensitive devices such as touch panels include a conductive faceplate. A touch anywhere on this conductive faceplate changes electrical impedances on a conductive coating of the faceplate. These impedances when measured can be used to indicate not just that a touch occurred but also the location of the touch on the touch sensitive surface.